Oxide thin film field effect transistor (Oxide TFT) is used in a back panel of a liquid crystal display (LCD) as a driver for a pixel region to control rotation of the liquid crystal such that different grey scales are produced in the pixel region. In an active matrix organic light-emitting diode (AMOLED) panel, the oxide TFT is used for controlling the brightness of an electroluminescent light emitting layer, so that different gray scales are produced in the pixel region. As illustrated in FIGS. 1A to 1F, the processes for manufacturing a double-bottom-gate OTFT are as follows:
First, a layer of metal (typically, molybdenum metal) is deposited on a substrate, and a double-bottom-gate structure including two identical gate metal layers 101 i.e. Gate layer 101, is formed after etching, as illustrated in FIG. 1A;
Second, a layer of insulating material is applied above the Gate layer 101 so as to form a gate insulating (Gate Insulator, GI) layer 102, as illustrated in FIG. 1B;
Third, indium gallium zinc oxide (IGZO) is applied above the GI layer 102 so as to form an IGZO layer 103 as illustrated in FIG. 1C, and the IGZO layer may be used as the semiconductor layer of the OTFT;
Fourth, an inorganic nonmetallic material is deposited on the IGZO layer 103, and a blocking layer 104 is formed after etching the material, as illustrated in FIG. 1D; the blocking layer is used to prevent the IGZO layer from being damaged during subsequent etching a source metal layer and a drain metal layer;
Fifth, a layer of metal is deposited above the blocking layer 104, and a source metal layer 106 as a source electrode, a drain metal layer 105 as a drain electrode, and an intermediate metal layer 107 are formed after etching the layer of metal, respectively, as illustrated in FIG. 1E;
Sixth, PVX is deposited above the source metal layer, the drain metal layer and the intermediate metal layer, and an insulating layer 108 is formed, as illustrated in FIG. 1F.
The operation principle of the OTFT is described as follows by taking a double-bottom-gate OTFT in an AMOLED as an example.
Firstly, a digital signal, i.e., Data signal, is applied to the source metal layer; Secondly, a voltage is applied to the gate metal layer; when the voltage is greater than a certain value, the IGZO layer becomes to a conducting state and carriers are generated therein. At this time, the digital signal applied to the source metal layer can be transmitted to the drain metal layer through the carriers, and the electroluminescent light emitting material connected with the drain emits light.
However, the inventors have found that, the OTFT with the double-bottom-gate structure produced in the prior art occupies a relatively large area in the pixel region. For example, if the OTFT has an aspect ratio of W/L=18/9, then it can be known that the width of the double-gate has a minimum width of 40 μm. As such, it will exert a large influence on the aperture ratio of an array substrate with a pixel size of 50×200 μm. The aperture ratio refers to a ratio of the area of an actual light-transmitting region to the total area of the unit pixel within a unit pixel. Obviously, the higher the aperture ratio is, the higher the light transmittance is. Therefore, if the area of the double-gate area is larger, the aperture ratio is smaller and the light transmittance is lower.